THE FLAMES ARE HIDDEN, but the poisonous gases wafting from deep fractures in the earth in Centralia, Pennsylvania, belie the stubborn fire burning below.

The fire started at the Centralia town dump in May 1962, where burning trash lit an exposed coal seam at the mouth of a mine. The fire followed the seam deep into the earth, and numerous attempts were made to extinguish it, including digging long trenches and pouring cement, wet sand, and other materials to starve the fire of oxygen. Coal fires are uniquely difficult to fight, however; they can be intensely hot and difficult to access. The Centralia efforts failed, and the fire continued to spread through a honeycomb of tunnels and caverns. After spending nearly $7 million on the effort, the government admitted defeat in the 1980s and ceased all efforts to extinguish the Centralia fire. Scientists have estimated that there is enough material left in the mine to burn for another quarter century.

As Smithsonian Magazine pointed out in a 2005 article, the residents of Centralia at first didn’t seem to mind the fire burning beneath them. Many no longer had to shovel snow; some could even grow tomatoes year-round in the warm ground. But the honeymoon was short lived. Residents began passing out from carbon monoxide leaking from the ground; Route 61, the main road into town, dropped eight feet; vegetation died; and in 1981, a 12-year-old boy toppled into a sink hole, saving himself by clinging to a tree root until a cousin pulled him to safety. The town was becoming increasingly unfit for habitation.

In 1983, Congress approved $42 million to purchase residents’ property and demolish every house in town. All but 63 of Centralia’s 1,100 residents had left by 1990, and nearly all of the buildings had been razed, leaving behind an empty grid of roads and driveways. The few residents who chose to remain waged a legal battle to prevent the government from taking their homes by eminent domain. In 2013, the eight remaining residents settled their lawsuit against the state, with each receiving cash payouts of $349,500 and the right to live out the rest of their lives in Centralia.

Centralia isn’t alone. Anupma Prakash, a geologist at the University of Alaska at Fairbanks, told Smithsonian that the prevalence of coal-mine fires globally is “a worldwide catastrophe” from an environmental perspective, contaminating soil, spewing toxins into the air, and worsening global warming. More than 30 of these fires now burn in Pennsylvania alone; hundreds more burn throughout the United States, and thousands burn worldwide. Experts say China has the most, with hundreds of coal fires burning in a 1.5 million-square-mile area in the north of the country.

Most coal fires are accidently set during mining operations, or as an unintended consequence of slash-and-burn deforestation. Some occur naturally when coal fields are exposed at the surface through erosion and lit by chemical reaction, lightning, or wildfire. The longest-burning coal fire is at Australia’s Mount Wingen, or Burning Mountain, which scientists estimate has burned for 6,000 years.